A conventional voltage-controlled oscillator comprises a voltage-controlled variable delay unit which can control the delay time for which a differential signal is transmitted from a pair of reference input signal lines to a pair of reference output signal lines by a control signal, the voltage-controlled variable delay unit comprising a plurality of amplifier elements with which a pair of input signal lines, a pair of output signal lines and one or more control signal line are provided, the plurality of amplifier elements are linearly connected to connect the pair of input signal lines and the pair of output signal lines; and exclusive OR circuits to obtain a doubled signal by utilizing a phase difference of signals obtained from the respective pair of output signal lines from the voltage-controlled variable delay unit, wherein the voltage-controlled variable delay units and the exclusive OR circuits are connected in the form of a pyramid by means of the pairs of output signal lines.
In the conventional voltage-controlled oscillator, when the control signal line is controlled such that the phase difference between the periodic signal inputted to the pair of reference input signal lines and the periodic signal outputted from the pair of reference output signal lines is 180 degrees, the periodic signal with a quadrupled frequency of 4.times.f(if the frequency of the periodic signal is f) is obtained from the pair of output signal lines.
However, since the dispersion in the quality of the amplifier element or exclusive OR circuit directly affects the jitter in the doubled signal obtained from the pair of output signal lines, the doubled or quadrupled signal therefrom trends to include a considerable jitter.